Modern smart TVs could hypothetically overlay virtually anything, however, you would not be able to overlay on to another “app” or channel as it opens cans of worms. For example, Roku had a lot of fraud from channels which showed one thing to the viewer while downloading ads in the background to persuade the backend the ads had been seen.

Back in the digital satellite era there was a transition where it was possible for the interactive content from one channel to be overlaid on the video of another as long as both were on the same satellite and underlying channel (a bit like “frequency” but not always 1:1). This is because digital TV multiplexes multiple videos for different user visible channels into a single stream with their interactive gunk, and the gunk can switch video streams. The fun part was this bandwidth is auctioned, and because every shady gambling company (half of cyprus it seems) wanted to be overlaid on sports the most expensive bandwidth was any spare around the sports channels. Not sure anyone ever made use of this in the end though.